1. Field of the Invention
In most prior applications, emission filaments used in scientific instruments have been constructed from pure Rhenium with purity levels exceeding 99.99%. Rhenium has been the material of choice due to a basic resistance to oxidation and good emission qualities. However, Rhenium has also presented a few unique problems and other issues over the many years of usage thereof as emission filaments. Rhenium tends to be quite a soft material and has a tendency to warp or otherwise deform during emission especially when experiencing ele2vated temperatures. This characteristic can present a problem for various scientific instruments where the focal point of the electron beam generated by the filament is quite critical and any movement of the filament causes a decrease in the sensitivity of the beam and, consequently, a decrease in the sensitivity of the scientific instrument.
Previously most filaments have also been made from tungsten or from an alloy of tungsten such as 97% tungsten and 3% Rhenium. Although these alloys are still being used in some instruments, many manufactures have refrained from using such tungsten alloys due to the tendency of rapid oxidation of the tungsten in the presence of any traces of oxygen in the environment resulting in the formation of significant accumulations of tungsten oxide on the surfaces of the filaments which severely compromises operation.
2. Description of the Prior Art
Many patents have been granted detailing various configurations of emission filaments for use in scientific instruments such as shown in U.S. Pat. No. 3,318,683 patented May 9, 1967 to E. L. Foster, Jr. et al and assigned to Battelle Development Corporation on a “Refractory Metal Powders”; and U.S. Pat. No. 3,530,327 patented Sep. 22, 1970 to R. J. Zollweg et al and assigned to Westinghouse Electric Corporation on “Metal Halide Discharge Lamps With Rare-Earth Metal Oxide Used As Electrode Emission Material”; and U.S. Pat. No. 3,623,860 patented Nov. 30, 1971 to R. F. Cheney et al and assigned to GTE Sylvania Incorporated on a “Tungsten-Rhenium Alloy Powder”; and U.S. Pat. No. 3,731,095 patented May 1, 1973 to T. Komoda and assigned to Hitachi, Ltd. on an “Electron Gun Device Of Field Emission Type”; and U.S. Pat. No. 3,916,202 patented Oct. 28, 1975 to R. F. Heiting et al and assigned to General Electric Company on a “Lens-Grid System For Electron Tubes”; and U.S. Pat. No. 3,984,692 patented Oct. 5, 1976 to G. P. Arsenault and assigned to Massachusetts Institute of Technology on an “Ionization Apparatus And Method For Mass Spectrometry”; and U.S. Pat. No. 3,988,629 patented Oct. 26, 1976 to J. E. White et al and assigned to General Electric Company on a “Thermionic Wick Electrode For Discharge Lamps”; and U.S. Pat. No. 4,045,247 patented Aug. 30, 1977 to J. F. Morris and assigned to The United States of America as represented by the Administrator of the National Aeronautics and Space Administration on a “Thermocouples Of Tatalum And Rhenium Alloys For More Stable Vacuum-High Temperature Performance”; and U.S. Pat. No. 4,367,429 patented Jan. 4, 1983 to V. Wang et al and assigned to Hughes Aircraft Company on “Alloys For Liquid Metal Ion Sources”; and U.S. Pat. No. 4,540,884 patented Sep. 10, 1985 to G. C. Stafford et al and assigned to Finnigan Corporation on a “Method Of Mass Analyzing A Sample By Use Of A Quadrupole Ion Trap”; and U.S. Pat. No. 4,599,869 patented Jul. 15, 1986 to G. A. Ozin et al on a “Cryogenic Deposition Of Catalysts”; and U.S. Pat. No. 4,994,711 patented Feb. 19, 1991 to J. N. Natossian and assigned to Hughes Aircraft Company on a “High Brightness Solid Electrolyte Ion Source”; and U.S. Pat. No. 5,028,791 patented Jul. 22, 1991 to A. Koshiishi et al and assigned to Tokyo Electron Ltd. on an “Electron Beam Excitation Ion Source”; and U.S. Pat. No. 5,084,606 patented Jan. 28, 1992 to J. M. Bailey et al and assigned to Caterpillar Inc. on an “Encapsulated Heating Filament For Glow Plug”; and U.S. Pat. No. 5,220,167 patented Jun. 15, 1993 to L. Brown et al and assigned to Carnegie Institution of Washington on a “Multiple Ion Multiplier Detector For Use In A Mass Spectrometer”; and U.S. Pat. No. 5,493,115 patented Feb. 20, 1996 to M. L. Deinzer et al and assigned to The State of Oregon acting by and through the State Board of Higher Education on behalf of Oregon State University on “Methods For Analyzing A Sample For A Compound Of Interest Using Mass Analysis of Ions Produced By Slow Monochromatic Electrons”; and United States Patent No. 5,506,412 patented Apr. 9, 1996 to S. E. Buttrill, Jr. on a “Means For Reducing The Contamination Of Mass Spectrometer Leak Detection Ion Sources”; and U.S. Pat. No. 5,543,625 patented Aug. 6, 1996 to B. S. Johnson et al and assigned to Finnigan Corporation on a “Filament Assembly for Mass Spectrometer Ion Sources”; and U.S. Pat. No. 5,756,996 patented May 26, 1998 to M. E. Bier et al and assigned to Finnigan Corporation on an “Ion Source Assembly For An Ion Trap Mass Spectrometer And Method”; and U.S. Pat. No. 6,060,829 patented May 9, 2000 to M. Kubon et al and assigned to U.S. Philips Corporation on a “Metal Halide Lamp With Rhenium Skin On Tungsten Electrode”; and U.S. Pat. No. 6,162,552 patented Dec. 19, 2000 to B. P. Bewlay et al and assigned to General Electric Company on a “Rhenium-Coated Tungsten-Based Alloy And Composite Articles And Method Therefor”; and U.S. Pat. No. 6,359,386 patented Mar. 19, 2002 to G. L. Von Morgen et al and assigned to U.S. Philips Corporation on an “Electric Lamp With Metal Shell”; and U.S. Pat. No. 6,404,130 patented Jun. 11, 2002 to R. J. Dinter and assigned to Patent-Treuhand-Gesellschaft fuer elektrische Gluehlampen mbH on a “Metal Halide Lamp With Fill Efficient Two-Part Lead-Through”; and U.S. Pat. No. 5,749,803 patented Jun. 15, 2004 to R. J. Adams and assigned to Honeywell International, Inc. on “Oxidation Resistant Rhenium Alloys”; and U.S. Pat. No. 6,812,626 patented Nov. 2, 2004 to P. Perlo et al and assigned to C.R.F. Scoieta Consortile per Azioni on “Light Source With Matrix Of Microfilaments”; and U.S. Pat. No. 6,821,313 patented Nov. 23, 2004 to R. J. Adams and assigned to Honeywell International, Inc. on Reduced Temperature And Pressure Powder Metallurgy Process For Consolidating Rhenium Alloys”; and U.S. Pat. No. 6,979,818 patented Dec. 27, 2005 to A. A. Scheidemann et al and assigned to OI Corporation on a “Mass Spectrometer For Both Positive And Negative Particle Detection”; and U.S. Pat. No. 7,185,527 patented Mar. 6, 2007 to B. Lin and assigned to Agilent Technologies, Inc. on “Protecting Filaments Of A Thermal Conductivity Detector”; and U.S. Pat. No. 7,235,796 patented Jun. 26, 2007 to E. Kolodney et al and assigned to Technion Research & Development Foundation Ltd. on a “Method And Apparatus for The Generation Of Anionic And Neutral Particulate Beams And A System Using Same”; and U.S. Pat. No. 7,270,782 patented Sep. 18, 2007 to R. J. Adams and assigned to Honeywell International, Inc. on a “Reduced Temperature And Pressure Powder Metallurgy Process For Consolidating Rhenium Alloys”; and U.S. Pat. No. 7,247,495 patented Jul. 24, 2007 to A. Amirav on a “Mass Spectrometer Method And Apparatus For Analyzing A Sample In A Solution”; and U.S. Pat. No. 7,309,860 patented Dec. 18, 2007 to T. Baba et al and assigned to Hitachi High-Technologies Corporation on a “Mass Spectrometer”; and U.S. Pat. No. 7,329,864 patented Feb. 12, 2008 to Y. Wang on “Mass Spectrometry With Multiple Ionization Sources And Multiple Mass Analyzers”; and U.S. Pat. No. 7,442,920 patented Oct. 28, 2008 to A. A. Scheidemann et al and assigned to O.I. Corporation on an “Optical Bench For A Mass Spectrometer System”; and U.S. Pat. No. 7,460,225 patented Dec. 2, 2008 to V. Karanassios on “Miniaturized Source Devices For Optical And Mass Spectrometry”; and U.S. Pat. No. 7,462,824 patented Dec. 9, 2008 to Y. Wang on a “Combined Ambient Desorption And Ionization Source For Mass Spectrometry”; and U.S. Pat. No. 7,485,873 patented Feb. 3, 2009 to B. W. Ward et al and assigned to ALIS Corporation on “Ion Sources, Systems And Methods”; and United States Publication No. 2005/0238522 published Oct. 27, 2005 to T. A. Leonhardt et al and assigned to Rhenium Alloys, Inc. on “Binary Rhenium Alloys”.